Abstract

Background

Female animals are often able to store sperm inside their body - in some species even
for several decades. The molecular basis of how females keep non-own cells alive is
largely unknown, but since sperm cells are reported to be transcriptionally silenced
and, therefore, limited in their ability to maintain their own function, it is likely
that females actively participate in sperm maintenance. Because female contributions
are likely to be of central importance for sperm survival, molecular insights into
the process offer opportunities to observe mechanisms through which females manipulate
sperm.

Results

We used the honeybee, Apis mellifera, in which queens are highly polyandrous and able to maintain sperm viable for several
years. We identified over a hundred proteins representing the major constituents of
the spermathecal fluid, which females contribute to sperm in storage. We found that
the gel profile of proteins from spermathecal fluid is very similar to the secretions
of the spermathecal gland and concluded that the spermathecal glands are the main
contributors to the spermathecal fluid proteome. A detailed analysis of the spermathecal
fluid proteins indicate that they fall into a range of different functional groups,
most notably enzymes of energy metabolism and antioxidant defense. A metabolic network
analysis comparing the proteins detected in seminal fluid and spermathecal fluid showed
a more integrated network is present in the spermathecal fluid that could facilitate
long-term storage of sperm.

Conclusions

We present a large-scale identification of proteins in the spermathecal fluid of honeybee
queens and provide insights into the molecular regulation of female sperm storage.